On 11/13/2017 08:54 PM, TSUBOTA Masami wrote:
Dear Rietvelters,
I'd like to introduce our following article.
https://www.nature.com/articles/s41598-017-15766-y
Accuracy of refinement parameters in the Rietveld method is not so good.
We have carefully investigated the reason, focusing on the peak-shift.
Our results show that a proportional unit-cell compared to the true one
is obtained in the conventional Rietveld method. We propose an additional
criterion to obtain the true lattice parameters accurately.
Hope this might be useful or interesting to you.
Masami,
The manuscript is very interesting, and appears to provide useful information
regarding the accuracy of lattice constants.
That said, why did you choose the ad-hoc method of Howard for compensating for
peak asymmetry, which is largely due to axial divergence? The method of Finger,
Cox and Jephcoat ("A correction for powder diffraction peak asymmetry due to
axial divergence", J. Appl. Cryst. (1994). 27, 892-900) applies the optics of
the diffractometer to describe the asymmetry, AND the associated peak shift.
Yes, the method is computationally intensive, but it is physically superior to
merely adding sums of Gaussians. For most studies using small aperture slits
with minimal asymmetry, it probably does not matter; however, your study in
which a great deal is made of peak shifts, should use the best methodology.
Sincerely,
Larry
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